1. Field of Invention
The present invention relates to an emulating device, and more particularly, to a channel emulating device adapted to multiple-input multiple-output (MIMO) transmission systems.
2. Related Art
Accompanying to the progress of the technology, the wireless transmission-technology has been continuously developed and has tightly combined with the daily life. The electronic products such as mobile phones, personal digital assistants (PDAs), personal computers, and the like have brought a more convenient environment. In the age of the mass information flow, the demand on the-wireless transmission gets higher and higher.
A wireless communication system having a higher efficiency and a higher capability are needed in order to enhance the information transmission quality and the signal covering range and to implement the reliable and stable transmission. A MIMO transmission system is one of the wireless communication systems. As shown in FIG. 1, the MIMO wireless transmission system 1 includes m transmitting antennas T1, T2, . . . , Tm disposed at a wireless access point 11, and n receiving antennas R1, R2, . . . , Rn disposed at a receiver station 12. Thus, a MIMO channel 13 is built in the space, and the transmitting antennas T1, T2, . . . , Tm transmit signals to the receiving antennas R1, R2, . . . , Rn through the MIMO channel 13 so as to enhance the transmission efficiency and satisfy the requirement by way of antenna diversity, beam forming or spatial multiplex. This system may be expressed as:
      (                                        x            ⁢                                                  ⁢            1                                                            x            ⁢                                                  ⁢            2                                                            x            ⁢                                                  ⁢            3                                                ⋮                                                  xn                                            )    =                              (                                                                      h                  ⁢                                                                          ⁢                  11                                                                              h                  ⁢                                                                          ⁢                  12                                                                              h                  ⁢                                                                          ⁢                  13                                                            ⋯                                                              h                  ⁢                                                                          ⁢                  1                  ⁢                  m                                                                                                      h                  ⁢                                                                          ⁢                  21                                                                              h                  ⁢                                                                          ⁢                  22                                                                              h                  ⁢                                                                          ⁢                  23                                                            ⋯                                                              h                  ⁢                                                                          ⁢                  2                  ⁢                  m                                                                                                      h                  ⁢                                                                          ⁢                  31                                                                              h                  ⁢                                                                          ⁢                  32                                                                              h                  ⁢                                                                          ⁢                  33                                                            ⋯                                                              h                  ⁢                                                                          ⁢                  3                  ⁢                  m                                                                                    ⋮                                            ⋮                                            ⋮                                            ⋮                                            ⋮                                                                                      hn                  ⁢                                                                          ⁢                  1                                                                              hn                  ⁢                                                                          ⁢                  2                                                                              hn                  ⁢                                                                          ⁢                  3                                                            ⋯                                                              hnm                                                                                )                ⁢                  (                                                                      s                  ⁢                                                                          ⁢                  1                                                                                                      s                  ⁢                                                                          ⁢                  2                                                                                                      s                  ⁢                                                                          ⁢                  3                                                                                    ⋮                                                                                      sm                                                                                )                    +                        (                                                                      v                  ⁢                                                                          ⁢                  1                                                                                                      v                  ⁢                                                                          ⁢                  2                                                                                                      v                  ⁢                                                                          ⁢                  3                                                                                    ⋮                                                                                      vn                                                                                )                ⁢                                  ⁢        Or        ⁢                                  ⁢        x              =          Hs      +      v      wherein input signals s1, s2, . . . , sm are respectively emitted by the transmitting antennas T1, T2, . . . , Tm, output signals x1, x2, . . . , xn are respectively received by the receiving antennas R1, R2, . . . , Rn, the H matrix denotes an environmental matrix of the MIMO channel 13, and noises v1, v2, . . . , vn are received by the receiving antennas R1, R2, . . . , Rn.
More and more electronic products using the MIMO technology have become available in the market. Tests have to be performed before the products are mass-produced. The conventional testing method is to implement the portion of the H matrix using a testing system. As shown in FIG. 2, a testing system 2 is disposed between a testing device 3 and a device-under-test 4. The testing device 3 generates m input signals s1, s2, . . . , sm. The device-under-test 4 receives n output signals x1, x2, . . . , xn. The testing system 2 includes m first power splitters 21, m×n power attenuators/phase shifters 22 and n second power splitters 23. The first power splitters 21 respectively receive the input signals s1, s2, . . . , sm generated by the testing device 3 and generate n integrated signals I. The power attenuators/phase shifters 22 respectively receive the integrated signals I, adjusts the power or phase of the integrated signals I, and then generates n parameter signals P. The second power splitters 23 respectively receive the n parameter signals P and output the output signals x1, x2, . . . , xn to the device-under-test 4.
In the prior art, the testing system must have m×n power attenuators/phase shifters to emulate various transmission conditions when m input signals and n output signals exist. Consequently, the system will be very huge and complicated, and the manufacturing cost is also high. Thus, it is an important subject to provide a simple and low-cost device for emulating the MIMO transmission system.